This invention relates generally to the dispensing of fluid materials onto substrates. More particularly, the invention relates to the detection and/or monitoring of a bead of material which has been deposited onto a substrate. Specifically, this invention is applicable for the detection of the presence of voids, gaps, and other discontinuities associated with a deposited bead of material, such as, for example, a bead of an adhesive, sealant, or caulk, as well as determining other qualities of the bead, such as its height; cross-section or the amount of material dispensed therein. This invention is especially useful in the monitoring of a bead of material dispensed onto the periphery of window glass, such as a windshield or other glass element, for an automobile or other vehicles, in preparation of adhesively bonding the glass to the body flange of the vehicle.
The presence of an air bubble passing through a nozzle of a dispensing system or a reduction in the material supply pressure may cause a discontinuity in the bead deposited upon the substrate. If the air bubble or the reduction in the material supply pressure is small, the effect on the resulting bead may be minimal. However, if the air bubble is large or the material supply pressure is insufficient, the effect may produce a significant discontinuity in the bead or a bead having an insufficient cross-section. In some applications, discontinuities in the bead may not be critical, however, in others they may be. For example, discontinuities in a bead of the adhesive/sealant applied to a windshield may not only affect its ability to act as a moisture barrier, but it also may affect the strength of the bond of the windshield to the vehicle.
Attempts have been made to detect gaps in the dispensed bead automatically as opposed to an operator's visual inspection. For example, U.S. Pat. No. 4,662,540 to Schroter illustrates one attempt to detect the presence of air bubbles in sealants, mastics, and adhesives. In this system, a pressure transducer produces an electrical signal which corresponds to the instantaneous pressure of the fluid. This electrical signal is then differentially amplified and compared to a threshold. U.S. Pat. No. 5,086,640 to Nagata, et al. illustrates another attempt to detect a breakage or other discontinuity in the bead by monitoring the vibration of the dispenser. Both of these patents attempt to detect a discontinuity in the bead before the bead is actually deposited onto the substrate. Neither of these two patents actually monitor the bead after it has been deposited onto the substrate. Rather, they infer that a discontinuity has occurred as opposed to actually verifying that a discontinuity has actually occurred.
Although not in the assembly of automobile glass, attempts have been made to monitor a bead of material after it has been dispensed onto a substrate. For example, U.S. Pat. No. 5,026,989 monitors energy radiating from material dispensed onto a substrate utilizing an infrared sensor. However, this device must be used with a heated adhesive, such as a hot melt adhesive. It therefore would not be useful with room temperature adhesives. German Utility Patent G 91 10 924.8 illustrates directing a beam of light onto a substrate before the adhesive is applied and directing the beam of light onto the substrate after the drop of adhesive has been applied. This device monitors whether or not a drop of adhesive has been applied to a substrate as opposed to monitoring the complete bead of material. This device requires a reflective substrate, such as metal and may not be suitable for glass.
While gaps or complete breakages of the bead are undesirable, other defects of the bead may also affect its performance. For example, voids in the extruded bead, such as through holes, may also affect the ability of the bead to act as a moisture barrier and/or affect the strength of the bond of the window glass to the vehicle. Similarly, beads that are continuous, but not of a sufficient height or cross-section, may also be undesirable. In like manner, beads exceeding a certain height may also be undesirable. Therefore, it is desirable to be able to determine not only discontinuities in the bead, but also to detect voids and those beads not falling within certain limits. Up until now, this has not been possible.